In biochemical, biological or genetic laboratories the problem of bringing small quantities of a material to a defined temperature and to keep it at this temperature during a certain time is encountered very often. Devices for this task are well known and are offered commercially. Liquid baths, especially water baths controlled by thermostats are well known devices. They generally consist of a vessel, mostly containing a volume of several litres, which is equipped with an electric heating device, a stirrer and sometimes with a circulating pump. The heating device can be controlled by a thermostat in such a manner that the temperature of the circulated liquid is hold at a predetermined temperature. In some cases a cooling device for the liquid bath, by which the temperature of the liquid can be brought to temperatures below ambient temperature, is offered as well. Such a liquid bath can also be used as a cryostat. In general, the cooling device for such cryostats consists of a conventional cooling machine, working by compression or absorption of a cooling medium.
Liquid baths, which, by heating or cooling can be hold at constant temperature are useful and practical to handle for many laboratory tasks. They are suited both for the handling of samples in vessels, which can be put directly into the liquid bath and also for heating or cooling samples through externally circulating the heat transporting liquid.
For heating samples of different volume, especially for liquid samples there also exist electric heating plates, which in some cases may be equipped with a temperature sensor and a thermostat. Heating plates additionally equipped with a rotating permanent magnet are known as well. By putting a magnetic rod into the sample, this latter can be stirred while being heated or cooled.
However a disadvantage of all laboratory thermostats with a liquid bath as described above is their heavy weight and great volume. Compared with the volume of the samples to be heated or cooled, their need for energy is rather high as well. The heating plates commercially available, with or without a stirring device, by their nature are only suited where the temperature of the sample is to be hold above room temperature.
For the biochemical, biological or genetic laboratory, for instance for work with living cells or cell components such as protoplasts or cell nuclei or with living tissues, embryos and organs, cycles are sometimes demanded, whose temperatures are situated partly below and partly above room temperature. Compared to practice in the chemical or physical laboratories the temperatures to be attained in general are not very much above or below room temperature. The typical range in the biological or biochemical laboratory may be between -5.degree. and +60.degree. C.
The conditions of the biological laboratory imply some special requirements in other respects as well: Some kinds of vessels which are used very often, such as the flat Petri disks, are not well suited for the use in a liquid bath; the alcohol, which is very often used as a cooling medium in liquid baths, is undesired in biological laboratories because of the activity of its vapour; restricted space, which is the rule in laminar air flow cabinets, calls for small apparatus. Maintaining sterility is very often an important requirement as well.
Water ice, which in the biological laboratory is used very often, has many disadvantages: It has to be constantly renewed and for its preparation needs a machine which is relatively expensive and spacious. Ice is difficult to be kept sterile; its handling, e.g. for Petri disks is sometimes not very practical. Its constant temperature of 0.degree. C. is a further disadvantage. Lower temperatures may be attained by adding salt, but the programming of temperature cycles remains difficult in this case as well.
It is the scope of this invention to create a laboratory apparatus especially suited to fulfill the needs of the biological, biochemical or genetic laboratory. It is easily manageable for heating or cooling samples of liquids or of biological material and for leading them through determined temperature cycles and its asks for only little room and energy. It is especially conceived to accomplish cycles with temperatures lying partially above and partially below room temperature. It is easy to sterilize and to be kept sterile. It can be equipped with the necessary devices to stir the samples, or, thanks to its small volume and weight, can even be installed on a conventional shaking machine. The separation into a working unit on the one side and a control unit on the other side is of special advantage for such cases.